Features and Benefits

Thin-bed mortar for producing brickwork from blocks made of aerated concrete or sand-lime


  • Long open time
  • Waterproof
  • Frost-resistant
  • Volume-stable
  • Easy to use
  • Amount required: approx. 1.3 kg/m2 and mm layer thickness

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For fixing blocks and slabs made of aerated concrete or sand- lime using the thin-bed method. For joint widths of 1 to 3 mm. For internal and external walls. For producing brickwork from aerated concrete blocks (grades G 2, G 4 and G 6). For trowelling blocks and slab made of sand- lime (indoor use).

Test certificate no. 220004236-05, MPA, NRW/Germany

Step by step

Substrate preparation


CT 21 adheres to all solid, load-bearing and clean substrates free of substances which may impair adhesion. Aerated concrete blocks and sand-lime bricks must have a rough, open-pored surface.



Sprinkle CT 21 into clean, clear water and stir until completely free of lumps. Observe the following mixing ratio: 1 part by volume of water to approx. 2.5 parts by volume of mortar or approx. 7.4 l of water for 25 kg of CT 21. CT 21 is workable for about 4 hours. Apply the mortar with a notched trowel, blockwork trowel or notched spreader using the combing technique. Observe the open time of approx. 10 minutes. The position of the blocks can be adjusted for approx. 5 minutes after placing.